Generally, a fine blanking method is generally well known as a method that can press mold a metal material with a high accuracy, so as to form a product having various shapes such as a car part or other such parts. According to the fine blanking method (which will be hereinafter referred to as “FB method”), a shearing force can be applied to a metal material with a high degree of accuracy even if the metal material has a relatively large thickness. Therefore, the product can be finished so as to have smooth cut surfaces (with a desired accuracy) without producing cracks and fracture surfaces therein. Thus, the FB method may produce a finished product having smooth cut surfaces.
More specifically, the FB method utilizes a hydraulic pressing machine in which various components can be hydraulically operated so as to permit complicated motion thereof. In particular, a work piece (the metal material) is clamped between a pad (a hold-down plate) and a die so as to be held therebetween. Therefore, when a punch cooperates with the die such that a shearing force can be applied to the work piece (when the clearance between the punch and the die is minimized), a relief force that acts in the work piece (i.e., an outward force that acts in a direction perpendicular to the shearing force) can be suppressed. Alternatively, an elongated projection (a V-ring) is formed between the pad and the die in order to increase the holding power of the pad and the die. In this case, the work piece can be held between the pad and the die while the retainer member bites into the work piece. Therefore, the relief force can be further reduced. As a result, the shearing force can be convergently applied to the work piece. This may lead to a high-accuracy processing of the work piece.
In addition, when a shearing force is applied to the work by means of the punch and the die, a bending force acts on the work piece due to the clearance between the punch and the die, so that an acting force (a spring-up force) can be applied to the work piece, which acts to urge the work piece to spring up from the punch. Therefore, in order to prevent the work piece from springing-up from the punch and to suppress the shearing force from dispersing, an ejector (a product retainer) is provided on the opposite side of the punch (so as to oppose the punch with interleaving the work piece therebetween), thereby suppressing the action of this spring-up force. In particular, the various components can be hydraulically operated in a complicated manner so as to provide a pressing condition in which the ejector can suppress the spring-up of the work piece while moderately applying the shearing force of the punch to the work piece.
A related technique is disclosed in, for example, JP 02-160125 A.